In Situ Synthesis of Ceramic Reinforcements for Carbon/CuCrZr Joints Brazed with Composite Fillers
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JMEPEG DOI: 10.1007/s11665-016-2398-4
In Situ Synthesis of Ceramic Reinforcements for Carbon/ CuCrZr Joints Brazed with Composite Fillers Yangwu Mao, Si Yu, Quanrong Deng, and Pei Zhao (Submitted August 7, 2016; in revised form September 30, 2016) Brazing of two kinds of carbon materials including graphite and carbon fiber-reinforced carbon composites to copper alloys has been realized with CuTiH2 + BN composite fillers. The microstructure characterization reveals that the ceramic reinforcements containing TiN particles and TiB whiskers have been synthesized by in situ reaction of BN additives with Ti discomposed from TiH2 in the composite filler. The filler layer of the joints is mainly composed of Cu-based solid solutions [Cu (ss)] and Ti-Cu intermetallics along with ceramic reinforcements. Furthermore, a continuous thin reaction layer mainly containing TiC is developed at the interface close to the carbon substrates. The growth of TiC layer is mainly controlled by the diffusion of carbon from the substrates into the liquid filler through the TiC layer formed. The interface evolution of the graphite/CuCrZr joints has been discussed. The electrical resistivity of the joining area is relatively low, which highly meets the requirement for the carbon commutator applications. Keywords
brazing, carbon, composites, interface, joining, metallic matrix, residual stress
1. Introduction Carbon materials are of great interest in many industrial applications due to their excellent properties such as low density, high thermal conductivity, and excellent thermal shock resistance. In some cases, applications of the carbon materials depend on the joining of them to metals (Ref 1-3). For example, fabrication of carbon commutator in automotive industry or carbon-based plasma facing components in fusion applications may rely on the joining of carbon materials to copper alloys (Ref 4, 5). As a reliable and convenient joining technique, brazing has been widely used in joining dissimilar materials. However, most non-active metals such as silver and copper show poor wettability on the carbon materials (Ref 5, 6). Therefore, the commercial brazes without reactive elements are unsuitable for brazing carbon materials to metals. In order to overcome this problem, surface modification of carbon materials (Ref 7-9) or the use of active brazes containing Cr or Ti (Ref 10-12) can be adopted. Furthermore, large residual stresses can be generated due to the mismatch of coefficient of thermal expansion (CTE) between carbon materials and copper alloys, leading to the deterioration of the properties of the joints (Ref 5). The residual stresses of ceramic/metal joints are expected to be relaxed by using stress-absorbing compliant metal interlayers or composite fillers composed of brazes and reinforcements with low CTE (Ref 13-18). The reinforcements, which can be added directly
Yangwu Mao, Si Yu, Quanrong Deng, and Pei Zhao, Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, Wuhan Institute of Technology, Wuhan 430073, China. Contact e-mail
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